The present invention relates to agricultural sprayers of pressurized liquids, and more particularly concerns an improved pump design for such a sprayer in which liquid is agitated and in which piston leakage is contained.
Pressurized discharge of various types of liquid insecticides, fertilizers, herbicides and other agricultural-type treatment liquid has been accomplished by directly pressurizing a pressure vessel that is mounted within a portable liquid container. Pressure is produced by a pump also connected to the container and pressure vessel. Liquid is drawn from the container, caused to flow under pressure into the pressure vessel and sprayed therefrom under control of a spraying valve.
Most sprayers need but do not provide agitation of container contents. Efficient spraying of agricultural insecticides, herbicides and the like requires control of the amount of insecticide dispensed. Manufacturers of spraying chemicals recommend preferred use rates for efficient application of the chemicals. These rates specify the amount of chemical to be used per acre. However, recommended rates can be met only if the spraying equipment is able to control the solution strength, in addition to controlling pressure and output flow rate. For some materials, solution strength depends on the amount of non-soluble but wettable particles maintained in suspension within the solution. In such suspensions, agitation is required to minimize precipitation of solid particles so as to maintain solution strength.
In many sprayers employing piston pumps, the life of the sprayer is often related directly to the life of the pump piston, because leakage of the liquid past a worn pump piston must be avoided. Liquids to be sprayed are often toxic and leakage from the sprayer may cause severe damage to the person of the operator or other contamination of operator or equipment. Moreover, new government regulations may restrict the amount of leakage that can be acceptable in a sprayer of toxic material. To increase the sprayer life and minimize the leakage problem, it has been suggested, as described in my prior application Ser. No. 616,012, referred to above, to replace the piston with a diaphragm pump which is not subject to the wear of the piston and which can be more readily and completely sealed for longer pump life. However, the diaphragm pump, although possessing a number of advantages, cannot provide as high an output pressure as a piston pump. Therefore, a piston pump is preferable to a diaphragm pump in many applications.
A sprayer having combined piston and diaphragm pumps for both high pressure discharge spraying and agitation by means of the action of the diaphragm is described in my co-pending application Ser. No. 845,631, referred to above, and is effective and satisfactory. Nevertheless, the unique cooperation of the tandem, dual pumping action of the adjoining piston pump and diaphragm pump introduces unique problems in maintaining high pressure for spray discharge, maximized assurance of leak containment, simplicity of assembly and ease of disassembly for repair or replacement.
Accordingly, it is an object of the present invention to provide a portable back sprayer having both high pressure discharge spraying and agitation by means of an improved dual pump assembly.